The present invention relates to a method of monitoring a catalyst and an apparatus therefor. More particularly, the present invention is directed to a method of predicting the efficiency of an automotive catalyst based on a catalyst lifetime temperature profile and a contamination measurement.
The efficiency of automotive catalysts must be known in order to indicate when a given vehicle exceeds allowable exhaust emission levels. As regulations become more stringent, reducing allowable exhaust emission levels, the accuracy for determining catalyst efficiency must be improved. At present, catalyst efficiency is measured using two oxygen sensors positioned before and after the catalyst. The difference in the oxygen content of the exhaust gas is then measured to determine the oxygen storage capacity of the catalyst, which is related to catalyst efficiency. Although this system is presently sufficient to measure catalyst efficiency, more stringent emissions standards will require improved sensor resolution and improved system accuracy.
A catalyst is a passive device which could function indefinitely under ideal conditions. The catalyst has two primary aging factors, thermal aging and contamination aging. Additionally, the lambda control frequency of the motor management system must be maintained above a threshold level in order to provide the optimum efficiency of the catalyst. If the parameters of temperature, time, lambda, and contamination are recorded over the life of the catalyst, the efficiency of the catalyst can be predicted with very high accuracy.
The present invention recognizes that the loss of efficiency in a catalyst is caused primarily by thermal aging and poisoning of the catalyst by exhaust contamination. With the use of an accurate exhaust gas temperature sensor, the time that the catalyst is operated above a predetermined threshold temperature may be recorded and weighted according to how far and how long above the threshold temperature the catalyst operates. This measurement may be used to create a lifetime temperature profile. Based on the known thermal aging characteristic of the catalyst, the catalyst efficiency can be accurately determined by comparing the measured lifetime temperature profile of the catalyst to its known thermal aging characteristic.